PHP

acf gallery

<?php 
$images = get_field('gallery');

if( $images ): ?>
    <ul>
        <?php foreach( $images as $image ): ?>
            <li>
                <a href="<?php echo $image['url']; ?>">
                     <img src="<?php echo $image['sizes']['thumbnail']; ?>" alt="<?php echo $image['alt']; ?>" />
                </a>
                <p><?php echo $image['caption']; ?></p>
            </li>
        <?php endforeach; ?>
    </ul>
<?php endif; ?>

acf gallery

<?php 
$images = get_field('gallery');
$size = 'full'; // (thumbnail, medium, large, full or custom size)
if( $images ): ?>
    <ul>
        <?php foreach( $images as $image_id ): ?>
            <li>
                <?php echo wp_get_attachment_image( $image_id, $size ); ?>
            </li>
        <?php endforeach; ?>
    </ul>
<?php endif; ?>

acf gallery

<?php 
$images = get_field('gallery');
if( $images ): ?>
    <ul>
        <?php foreach( $images as $image ): ?>
            <li>
                <a href="<?php echo esc_url($image['url']); ?>">
                     <img src="<?php echo esc_url($image['sizes']['thumbnail']); ?>" alt="<?php echo esc_attr($image['alt']); ?>" />
                </a>
                <p><?php echo esc_html($image['caption']); ?></p>
            </li>
        <?php endforeach; ?>
    </ul>
<?php endif; ?>